1. Field of the Invention
The present invention generally relates to an optical recording medium, and more particularly to an optical recording medium of write once read many type using organic dye film as a recording material.
2. Description of the Related Art
As a recording film of an optical disc of write once read many type, there is a film using organic dyes such as a cyanine group organic dye and a phthalocyanine group organic dye.
Recording information on this kind of optical disc of write once read many type is performed by condensing the laser beam to form a little spot on the organic dye film as the recording film, converting it to thermal energy, and forming a pit by changing the physical property such as the reflection coefficient, the planarity, the shape etc. of the recording film or by changing the chemical property.
More concretely, in the optical disc of write once read many type using the thermal discomposing property of the organic dye film, the information is recorded by sublimating the organic dye film by irradiating the laser beam, and forming an aperture.
In this kind of the optical disc of write once read many type by means of the aperture forming method, in order to easily perform the dispersion by the sublimation of the organic dye film, two substrates, to each of which the organic dye film (surface) is formed, are prepared. The organic dye films are opposed to each other and are bonded together through a spacer provided on internal and external circumferences of the substrate, so that the air sandwich structure is obtained.
In the optical disc of write once read many type by means of the aperture forming method by use of the above mentioned organic dye film, since a relatively large aperture is formed, there is a problem that the cross-talk amount is increased.
Since the air sandwich structure is employed, there is another problem that it is difficult to produce an optical disc having a relatively large area while retaining sufficient physical strength.
Further, there is another problem that the high recording power is required, since the heat energy is discharged by the sublimation to the space formed by the air sandwich structure at the time of recording.